Q4: Why is it that the moon appear yellow in the night sky? (Not Blue or other colors)

A: The light from the Moon is actually a reflection of the light coming from the Sun. The light coming from the Sun, on the other hand, is a part of a narrow band of wavelengths called the visible light spectrum (the part of the electromagnetic spectrum to which our eyes are sensitive – and the only band our eyes are sensitive to). This constitutes a spectrum of wavelengths that range from approximately 700 nm (0.7μm) to approximately 400 nm (0.4μm).

The Visible Light Spectrum. Retrieved from: http://science.hq.nasa.gov/kids/imagers/ems/visible.html

Each color corresponds to a wavelength. Red light has the longest wavelength, and violet light has the shortest one. The photons (smallest units of light) will possess higher energy if the wavelength is shorter. Conversely, the photons of light will possess lower energy if the wavelength is longer.

The energy possessed by the photons is very much associated with the scattering of light. The light (or the color) which has the shorter wavelength will most likely be scattered compared with the light (or the color) which has the longer wavelength.

Thus, as for the question why the Moon appears yellow, the answer is: BECAUSE OF OUR ATMOSPHERE. The Earth’s atmosphere contains tiny particles of dust and molecules that facilitate the scattering of light. The light with the shorter wavelengths (violet, blue) will be scattered, thus leaving the light with longer wavelengths (red, orange, yellow) to reach our eyes.

If you are under a dense or too polluted atmosphere, you may see the Moon in orange, for much light is already scattered away.

Note:
nm stands for nanometers.
μm stands for micrometers.


Prepared by: Ericka Jane Angeles